Spark plug



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Patented Nov. 27, 1945 UNITED- STATES PATENT OFFICE SPARK PLUG Chester Ciprlanl and Carl J. Eaton, Toledo, Ohio Application April 12, 1943, Serial No. 482,688 8 Claims. (Cl. 123-189) This invention relates to spark plugs, more It is a further object of this invention to prop r i l rly to the methods of holding and sealvide a resilient means positioned between the ing a ceramic insulator in the metallic shell of shell and the insulator or a spark plug which does not present insurmountable manufacturing One of the major problems involved in manug dlfllculties and which will be eflicacious in comfaeturing a spark plug, particularly a spark plug pensating for variations of expansion of the varifor use 1 in airplanes wherein shielding devices ous materials used in the spark plug throughout ar i c p r ted in the body of the spark plug. the temperature range of the en ine in which has been to maintain a, seal between a. ceramic the spark plug is used. insulator and the metallic shell in which the Other objects and advantages of this invention insulator is mounted. The metallic shell, and the relating to the arrangement, operation and funcceramic insulator mounted therein, have widely tion of the related elements of the structure, to varying coeiiicient of expansion which must be various details of construction, to combinations compensated in order that leakage will not deof parts and to economies of manufacture, will velop while the plug is in use in the motor of an b apparent to those skilled in the art upon airplane. The temperatures to which the spark consideration of the following description and plug is subjected while in use vary widely under appended claims, reference being had to the acthe operative conditions of the airplane motor companying drawing forming a part of this speciand, in order that the plug may be maintained flcation wherein like reference characters desigtight, the diil'erent expansion rates of the matenate corresponding parts in the several views.

rials used in the plu must be fully compensated Fig. 1 is a sectional elevation of a spark plug. for. One of the means used to compensate for Fig. 2 is an exploded view of the spark plug the very variable coemcient of expansion of the showing the different parts.

diil'erent materials has been a spring member Fig. 3 is an enlarged eievational view of the positioned between the insulator and the shell 215 spring member when in operative position. which oifers a resilient means to compensate for Fig. 4 is an enlarged perspective view of one these difierent expansion rates while the plug is of the members.

in use to maintain the required seal. In the prior Fig. 5 is an enlarged perspective view of the art different types of spring members have been spring member.

suggested for this purpose. Referring to the drawing, particularly to Fig. i,

This invention contemplates the provision of a metallic shell member In is provided having a spring member which is highly adaptable for an externally-threaded portion ll positioned bethis purpose, which is capable of being easily low an external shoulder I! on the shell. The manufactured, and which will result in a comexternally-threaded portion ii is adapted to cobination which is highly efllcacious in maintainoperate with an engine block (not shown) in ing a seal between the ceramic insulator and which a spark plug is positioned during opermetalllc shell of a spark plug, particularly of an ation. The shell I is provided with a hexagonal aviation spark plug. portion is above th shoulder I! for convenient It is, therefore, a principal object of this invenmanual manipulation in positioning the spark tion to provide a resilient means positioned beplug in the engine block. tween the metallic shell and the insulator of a Adjacent the extreme lower end of the threaded spark plug which is capable of compensating for portion II a recess I4 is provided in which is posivariations of expansion of the diilerent matetioned a ground electrode i5, preferably of the rials used in the fabrication of the spark plug 5 cloverleaf type, having three or more prongs coso as to maintain a seal between the parts under operating with a center electrode Hi to form the all operating temperatures to which the spark spark gap of the spark plug. The electrode I! plug will be subjected during use in an internal maybe brazed in the recess It, or attached thereto combustion engine. in any other convenient manner. The center It is a further object of this invention to proelectrode II is positioned in a ceramic insulator vide a resilient means for use between the insull, preferably of the alumina type, extending lator and the shell of a spark plug to maintain therethrough in a central bore terminating at a seal therebetween which is sufficiently flexible the upper end in a terminal ii. The center wire to prevent localization of bearing stresses upon it may be sealed in the center bore of the insuthe insulator and allow equalization thereof to later I! in any convenient manner, as, for examobviate breakage of the insulator. ple, by powder packing or the like. The insulator i1 is provided with an enlarged portion 12 to provide a pair of external shoulders 20 and 2i. The lower shoulder 20 is adapted to rest upon an internal shoulder 22 of the shell member it, being preferably positioned within the externallythreaded portion ii. A gasket member 22 is positioned between the external shoulder 20 of the insulator l1 and the internal shoulder 22 to provide a seal therebetween. The gasket is preferably formed of nickel or soft iron, or any other suitable material.

The upper portion of the shell Iii, adjacent the hexagonal portion l2 and above the external shoulder i2, is provided with an internallythreaded counterbore 24 which terminates in a second internal shoulder 26 in the shell it) which is preferably positioned below the external shoulder ll of the insulator. This allows the external shoulder 2| to project into the counterbore 24 as is clearly shown in Figs. 1 and 3.

Resting on the upper shoulder 2| of the insulator, a ring-like spring member 26 is provided having an aperture slightly smaller than the enlarged portion iii of the insulator so as to rest upon the extreme outer portion of the shoulder 2i by means of a curved surface 26a formed between the central aperture and the lower face 26b of the ring-like member. The outside diameter of the ring-like member is slightly smaller than the diameter of the internally-threaded bore 24 so as to fit between the internal bore and the insulator i1. The ring-like spring member 26 is preferably made of Inconel, or other metals having similar characteristics. Positioned above the ring-like spring member 26, a second ring-like member 21 is provided (shown in position in Fig. 3), being preferably made of steel or the like, and provided with the fiat upper surface which cooperates with the lower face 28 of an externally-threaded shielding sleeve 29 which will be described in greater detail hereinafter. The lower surface of the spring-like member 21 is given a tapered contour having the thickest portion 21a positioned adjacent its outer edge so as to contact the spring member 26 adjacent its perimetrical edge. The diameter of the spring member 26 is slightly smaller than the counterbore 24 so as to fit loosely therein, while the diameter of the ring-like member 21 is slightly larger than the spring member 26 and fits snugly into the counterbore 24 to center the insulator assembly in the shell ill.

The threaded portion of the metallic insulating sleeve 29 is adapted to engage with the internallythreaded counterbore 24 to advance the sleeve inwardly, by turning it with a wrench, engaging with a hexagonal portion 30 so as to apply force to the ring-like member 21 which, in turn, communicates force to the spring member 26 by the portion 21a which contacts the spring member adjacent its perimetrical edge. In this manner a distorting force can be applied to the spring member, causing the spring member to take a deflected position, as is most clearly shown in Fig. 3. The spring member 26, in turn, communicates the force, created by the threaded engagement, to the shoulder 2i of the insulator so as to thrust the lower shoulder 20 against the gasket 22 seated on the internal shoulder 22 of the shell. The gasket 22 is coined by this force to form an air-tight seal between the insulator i1 and the shell Iii. At the same time the spring member 26, being distorted by the force, creates a resilient cushion between the insulator I1 and the shell III which is capable of compensating for the different rates of expansion of the metal shell and the ceramic insulator.

In controlling the foot-pounds of torque applied to the hexagonal portion 26 of the sleeve 22, the

compressive force applied by the insulator i1 to the gasket 22 can be controlled within relatively close limits. It is essential that the compressive stress shall be maintained at a predetermined point which is suillcient to maintain a seal at the gasket 22 and not exceed a unit stress which will crush or cause breakage of the insulator at either of the shoulders 20 or 2i. In order to maintain this pressure at the desired value, it is convenient to braze, or otherwise permanently attach the shielding sleeve 22 to the shell Iii at a point above the threaded relation between the two parts as is shown by a fillet 2|. This creates a functionally-integral shell which originally comprised two parts, namely the shell iii and the shielding sleeve As is clearly shown in Fig. 1, the upper portion of the insulator i1 extends a considerable distance into the sleeve 29 and terminates at substantially a central location by the terminal i6 of the center wire i6. To insulate the high tension electric current which is in an ignition circuit contacting the terminal l8 by means well known in the art (not shown), an insulating sleeve 22 is provided fitting inside of the shielding sleeve 29. The lower end of the insulating sleeve 22 rests upon a gasket member 32 resting on a shelf 24 formed by the upper surface of the ringlike member 21 while the upper end is in contact with another gasket 26 contacting an inturned flange 26 formed on the upper end of the shielding sleeve 29. The gaskets 2'2 and 25 may be of insulating material, such as asbestos or the like, or may be formed of metal if desired and are adapted to hold the insulating sleeve 22 firmly in position in the shielding sleeve 29. The insulating sleeve 22 may be positioned within the shielding sleeve 22 prior to the time the shielding sleeve is placed in threaded engagement with the internal counterbore 24 with the flange 26 already in position or, if desired, it may be inserted after the shielding sleeve 29 is already in cooperative relation with the counterbore 24, in which case the flange 26 must be turned in after the insulating sleeve 22 is inserted in position.

The upper portion of the sleeve 29 is provided with a threaded portion 21 which is utilized to connect shielding devices containing high tension leads which form a part of the ignition circuit of the engine in which the spark plug is to be used. This structure is well known in the art and need not be described in detail.

It is to be understood that the above detailed description of the present invention is intended to disclose an embodiment thereof to those skilled in the art, but that the invention is not to be construed as limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the invention is capable of being practiced and carried out in various ways without departing from the spirit of the invention. The language used in the specification relating to the operation and function of the elements of the invention is employed for purposes of description and not of limitation, and it is not intended to limit the scope of the following claims beyond the requirements of the prior art.

What is claimed is:

1. In a device of the class described, a metallic shell having an internal shoulder and an insulator including a central electrode positioned in the shell having an enlarged portion adapted to rest on the internal shoulder, a ring-lik spring member adapted to cooperate with the enlarged portion of the insulator, the radial dimension of a portion of the spring member being substantially larger than its longitudinal dimension, and means on the shell to cooperate with the perimeter of the spring member to distort the spring member whereby the insulator is resiliently held against said internal shoulder.

2. In a device of the class described, a metallic shell having an internal shoulder and an insulator including a central electrode positioned in the shell having an enlarged portion adapted to rest on the internal shoulder, a ring-like spring member adapted to cooperate with the enlarged portion of the insulator and means cooperating with the shell and the perimeter of the spring member whereby the spring member may be subjected to a, torsional stress of a predetermined amount for longitudinal deflection in its radial extent to hold the enlarged portion of the insulator resiliently against said internal shoulder of the shell.

3. In a device of the class described, a metallic shell having an internal shoulder and an insulator including a central electrode positioned in the shell having an enlarged portion adapted to rest on the internal shoulder, a relatively flat ring-like spring member resting on the enlarged portion of the insulator to extend outwardly therefrom, and means cooperating with the shell and the perimeter of the spring member whereby the spring member may be subjected to torsional stress of a predetermined amount for longitudinal deflection in its radial extent to hold the enlarged portion 01. the insulator resiliently agaimt said internal shoulder of the shell.

4. In a device of the class described, a metallic shell having an internal shoulder and an insulator including a central electrode positioned in the shell having an enlarged portion adapted to rest on the internal shoulder, a ring-like spring member of substantially rectangular cross section resting on the enlarged portion of the insulator to extend outwardly therefrom, manually adjustable means on the shell to cooperate with the perimeter of the spring member to allow distortion of the spring membe to a predetermined amount to resiliently urge the enlarged portion of the insulator against the internal shoulder of the shell.

5. In a shielded spark plug, a metallic shell having an internal shoulder with an externallyihreaded end portion adjacent said shoulder and an internally-threaded portion on the opposite end of the shell, an insulator with a central electrode positioned in the shell having an enlarged portion adapted to rest on the internal shoulder, a ring-like spring member adapted to cooperate with the enlarged portion oi the insulator adapted fit within the internal threaded portion of the shell, a second ring-like member of substantially the same diameter as the spring member positioned above the spring member having a portion adapted to cooperate with the outer edge of the spring member, an externally-threaded sleeve adapted to cooperate with the internal threads of the sleeve-like member to contact the second ring-like member to apply force upon both the second ring-like member and the spring member to distort the spring member, and an insulating sleeve positioned within the sleeve-like member positioned around the insulator.

6. In a shielded spark plug, a metallic shell having an internal shoulder and a threaded end portion adjacent the shoulder, an insulator with a central electrode positioned in the shell having an enlarged portion adapted to rest on the internal shoulder, a ring-like spring member of substantially rectangular cross section adapted to cooperate with the enlarged portion of the insulator and to fit within the shell, a shielding sleeve adapted to fit within the shell adjacent the spring member adapted to apply force to the spring member to distort the spring member to hold the insulator resiliently against said internal shoulder, means to attach the sleeve member to the shell member, an insulating sleeve positioned inside the shielding sleeve to surround the upper end of the insulator above the enlarged portion, and means to hold the insulating sleeve in p sition.

7. In a shielded spark plug, a metallic shell having an internal shoulder and an externallythreaded end portion adjacent such shoulder, an insulator having a center electrode positioned in the shell having an enlarged portion adapted to cooperate with the internal shoulder, a ring-like spring member adapted to fit within the metallic shell having a curved contour adapted to rest upon the enlarged portion of the insulator, a second ring-like member of substantially the same diameter as the spring member cooperating with the perimeter of the spring member, a shielding sleeve adapted to fit into the metallic shell adjacent the spring member to cooperate with the second ring member and adapted to apply a distorting force to the spring member through the agency of the second ring-like member, means to hold the shielding sleeve in position in the shell, and an insulating sleeve positioned between the shielding sleeve and the upper portion of the insulator resting upon the second ring-like member, and means to hold the insulating sleeve in position in the shielding sleeve.

8. In a device of the class described, a metallic shell having an internal shoulder and a ceramic insulator including a central electrode positioned in the shell with an enlarged portion of the insulator adapted to rest on the internal shoulder, a toroidal spring member of substantially rectangular cross section with its largest dimension positioned radially, said spring member having an arcuate surface at its inner lower edge to cooperate with the enlarged portion of the insulator, and means cooperating with the shell and the upper perimetrical edge of the spring member to subject said spring member to a torsional stress to hold the enlarged portion 01' the insulator resiliently against the internal shoulder or the shell.

CHESTER CIPRIANI. CARL J. EATON. 

